Technical Field
The present invention relates to an engine starting apparatus capable of switching output characteristics of a starter including a wound-field-type brushed direct current (DC) motor.
Related Art
Conventionally, there is a desire for an idle-stop-enabled starter to reduce an engine restarting time as much as possible to improve the comfort of a driver or other occupants of a vehicle. A technique for reducing the restarting time includes increasing a cranking speed. Such a technique, however, in combination with good start-up performance at low temperatures where engine friction is high, necessitates use of a large in size and high power motor.
A known technique for increasing the cranking speed at restarting of the engine without increasing dimensions of the motor includes switching as needed between high-speed and high-torque characteristics.
For example, Japanese Patent Application Laid-Open Publication No. 2004-197719 discloses preparing a motor including a series coil and a shunt coil as field coils and switching between the high-speed and high-torque characteristics by an electronic control unit (ECU) controlling field current flowing through the shunt coil of the motor.
However, the technique as disclosed in Japanese Patent Application Laid-Open Publication No. 2004-197719 necessitates an energization current of a few amps to tens of amps to pass the current through the shunt coil, which leads to an increased cost of the ECU to control such a large current. Thus, an advantage of using a low cost brushed direct current (DC) motor may be diminished.
In consideration of the foregoing, exemplary embodiments of the present invention are directed to providing an engine starting apparatus capable of switching output characteristics of a starter with low cost without an electronic control unit (ECU) controlling field current flowing through field coils.